单选题

　　[完成句子]In Britain， robot sales appropriately peaked in 1984， but have been declining ever since. This is partly because， British wage rates are too low to make robots financially attractive and partly because engineers now have more experience with robots and are more aware of the difficulties of introducing them effectively.

　　Robots are less popular in Britain today partly because __________.

　　A、too much energy

　　B、based on American designs

　　C、they are too costly

　　D、they are not reliable